Uhm.
It wasn't an "attack" per-se.
It was some lunatic throwing a flaming whatever onto a moving train, which then caught another train on fire.
so basically more of a mass-murderer than a terrorist attack.
Had it been, say an attack carried out by some north koreans on the south korean train, I'm sure you'd hear quite a bit about it.
Basically it's an internal issue. The world doesn't hear about every train disaster here do they? We have more than a few each decade.
-Phil